(a) Field of the Invention
The present invention relates to a power train for an automatic transmission used in vehicles. More particularly, the invention relates to a power train for a 4-forward speed and 1-reverse speed automatic transmission.
(b) Description of the Related Art
Generally, automatic transmission systems for vehicles are provided with a transmission control unit (TCU) which automatically controls shift ratios according to changes in a running condition of the vehicle.
The typical TCU controls a plurality of friction elements provided in a gear train to either operative or inoperative states to select one of the three essential elements of a planetary gear set (i.e., a sun gear, a ring gear, or a planet carrier) to be an input element, a reaction element, or an output element, thereby controlling an output number of revolutions.
Particularly, a power train that can realize 4-forward speeds and 1-reverse speed comprises a plurality of heavy and large-sized clutches and brakes and a plurality of situationally inoperative friction elements.
FIG. 3 shows such a conventional power train.
The conventional power train includes first and second single pinion planetary gear sets 208 and 210. The first single pinion planetary gear set 208 includes a first sun gear 216, a first planet carrier 212, and a first ring gear 218. The second single pinion planetary gear set 210 includes a second sun gear 220, a second planet carrier 222, and a second ring gear 224.
Rotation power of an engine (not shown) is transmitted to an input shaft 206 via a torque converter 204, then is further transmitted to the first and second single planetary gear sets 208 and 210, and finally output through a transfer drive gear 214 connected to the first planet carrier 212. The shifting operation is realized while the rotation power of the engine passes through the first and second single planetary gear sets 208 and 210.
The first planet carrier is fixedly connected to the second ring gear 224 and the first sun gear 216 is variably connected to the input shaft 206 with a first clutch C1 interposed therebetween. The first clutch C1 is operated in all of the forward speed ratios.
The second planet carrier 222 is variably connected to the input shaft 206 with a second clutch C2 interposed therebetween, and the second sun gear 220 is variably connected to the input shaft 206 with a third clutch C3 interposed therebetween. The second clutch C2 is operated in third and fourth forward speed ratios, and the third clutch C3 is operated in a reverse range.
In addition, the second planet carrier 222 is fixedly connected to the first ring gear 218, and the combination of the second planet carrier 222 and the first ring gear 218 is connected to the transmission housing 226 with a first brake B1 interposed therebetween. The second sun gear 220 is connected to the transmission housing 226 with a second brake B2 interposed therebetween.
The power output through the transfer drive gear 214 is dispensed to a drive shaft through an intermediate shaft 228 and a differential 230.
In the above described prior power train, since the first clutch, the first brake, and the second brake are arranged such that they are spaced away from each other in an axial direction of the transmission housing, the longitudinal length of the housing is increased, limiting space for disposing one-way clutches which are used for improving shift quality.
Therefore, the present invention has been made in an effort to solve the above problems.
It is an objective of the present invention to provide a power train for an automatic transmission that is lightweight and compact in size, while at the same time providing improved power efficiency.
To achieve the above object, the present invention provides a power train for an automotive automatic transmission comprising a first planetary gear having a plurality of operating elements; a second planetary gear having a plurality of operating elements, at least one of the operating elements of the second planetary gear being fixedly connected to one of the operating elements of the first planetary gear; and a plurality of clutches, brakes, and one-way clutches for variable connecting elements of the first and second planetary gears to an input shaft, a transmission housing, or to each other, wherein at least two of the clutches are arranged spaced away from each other in a radial direction of the input shaft.
At least two of the brakes share a single retainer with each other, and one of the two clutches arranged spaced away from each other in a radial direction of the input shaft has a piston functioning as a retainer of the other of the two clutches.
The two clutches arranged spaced away from each other in a radial direction of the input shaft share a single spring with each other.
The plurality of operating elements of the first planetary gear comprise a first sun gear, a first planet carrier, and a first ring gear; the plurality of operating elements of the second planetary gear comprise a second sun gear, a second planet carrier, and a second ring gear; the first planet carrier is fixedly connected to the second ring; the plurality of clutches comprise first, second and third clutches for variably connecting the first sun gear, the second planet carrier, and the second sun gear to the input shaft, respectively, and a fourth clutch for variable connecting the second planet carrier to the first ring gear; the plurality of brakes comprise first and second brakes for connecting the second planet carrier and the second sun gear to the transmission housing; the plurality of one-way clutches comprise first and second one-way clutches for connecting the second planet carrier to the ring gear and the transmission housing; and the second and third clutches are the two clutches arranged spaced away from each other in a radial direction of the input shaft.
According to another aspect, the present invention provides an automotive automatic transmission comprising a first planetary gear having a plurality of operating elements; a second planetary gear having a plurality of operating elements, at least one of the operating elements of the second planetary gear being fixedly connected to one of the operating elements of the first planetary gear; and a plurality of clutches, brakes, and one-way clutches for variable connecting elements of the first and second planetary gears to an input shaft, a transmission housing, or to each other, wherein inner and outer races of the respective first and second one-way clutches of the plurality of one-way clutches share a single member with each other.
An outer race of the first one-way clutch is connected to the transmission housing by a spline.
The outer race of the second one-way clutch functions as a retainer of at least one of the brakes.
The inner and outer races of the respective first and second one-way clutches are separately formed and splined to each other to form the single member.
At least two of the clutches are arranged spaced away from each other in a radial direction of the input shaft.